Methods for producing stabilized solid thiocarbonate compositions

ABSTRACT

Encapsulating particles of solid thiocarbonate salts, esters and complexes with air- and water-impermiable coatings produces compositions having long-term stability.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of co-pending application Ser. No.07/290,992 filed Dec. 28, 1988 now U.S. Pat. No. 5,039,327 which was acontinuation-in-part of applications Ser. No. 253,139, filed Oct. 4,1988 now U.S. Pat. No. 4,908,143 and U.S. Ser. No. 260,912, filed Oct.21, 1988, now U.S. Pat. No. 4,908,142 both of which are hereinincorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to stabilized solid thiocarbonatecompositions and methods for producing same.

2. Background of the Invention

The chemistry of thiocarbonic acids and salts has been studied in somedetail, as indicated by O'Donoghue and Kahan, Journal of the ChemicalSociety, Vol 89 (II), pages 1812-1818 (1906); Yeoman, Journal of theChemical Society, Vol 119, pages 38-54 (1921); Mills and Robinson,Journal of the Chemical Society Vol. 128(II), pages 2236-2332 (1928) andby Stone et al in U.S. Pat. No. 2,893,835, dated Jul. 7, 1959.

According to O'Donoghue and Kahan, as far back as 1826 derivatives ofthiocarbonic acid were prepared by Berzelius, who reacted aqueoussolutions of hydrosulfides with carbon disulfide, the reactionsoccurring as in (1)

    2KHS+CS.sub.2 →K.sub.2 CS.sub.3 +H.sub.2 S          (1)

giving unstable solutions which yielded unstable crystalline salts.

Other thiocarbonates were prepared and further characterized byO'Donoghue and Kahan. Their paper, at page 1818, reports the formationof ammonium thiocarbonate by reacting liquid ammonia with cold alcoholicthiocarbonic acid prepared by dropping a solution of "calciumthiocarbonate" into concentrated hydrochloric acid to produce freethiocarbonic acid (H₂ CS₃). The "calcium thiocarbonate" utilized by theauthors is described as a double salt, including the calcium cation incombination with both the hydroxide and the trithiocarbonate anions. Inaddition to making free thiocarbonic acid, other compounds prepared byO'Donoghue and Kahan included the sodium, potassium, zinc and leadsalts. However, regardless of which of these salts were prepared, acommon characteristic was their relative instability, with the preparedcompounds breaking down and releasing carbon disulfide and hydrogensulfide and/or a metal sulfide, often in a matter of minutes.

The noted paper by Yeoman reports a further study of thiocarbonates(called trithiocarbonates therein) and also reports the preparation andproperties of perthiocarbonates (or tetrathiocarbonates) and derivativesof tetrathiocarbonic acid (H₂ CS₄). Yeoman reports on methods ofpreparing the ammonium, alkali metal and alkaline earth metal salts ofthese acid species. For example, Yeoman prepared ammoniumtrithiocarbonate by saturating an alcoholic ammonia solution withhydrogen sulfide and then adding carbon disulfide to precipitate theproduct salt. Ammonium perthiocarbonate was prepared in a similarmanner, except that after reacting the ammonia and hydrogen sulfide,elemental sulfur was added to form the disulfide, (NH₄)₂ S₂ ; addingcarbon disulfide immediately precipitated the product.

Yeoman states that "solutions of both ammonium trithiocarbonate andperthiocarbonate are very unstable" due to both decomposition to formthiocyanate as a product, and to "complete dissociation back intoammonia, hydrogen sulfide and carbon disulfide."

Considerable explanation is provided concerning the stability ofthiocarbonates, as exemplified by sodium trithiocarbonate andperthiocarbonate. Sodium trithiocarbonate solutions in water are said toremain stable only if oxygen and carbon dioxide are "rigidly excluded";the presence of oxygen causes decomposition to form carbon disulfide andthiosulfates, while carbon dioxide decomposes the solution to form acarbonate, elemental sulfur, carbon disulfide and hydrogen sulfide.Potassium trithiocarbonate behaves similarly, according to Yeoman.

Yeoman also attempted to prepare and characterize the stability ofthiocarbonate salts of four of the alkaline earth metals. Yeoman wasunable to prepare a "pure" calcium tri- or tetrathiocarbonate, but didobserve that the double salt of calcium trithiocarbonate which heprepared was more stable (probably because it was less hygroscopic) thanthe sodium or potassium thiocarbonates. The barium tetrathiocarbonatecould not be isolated, although Yeoman believed it existed in solution.Solid barium trithiocarbonate was found to be stable, although it wasalleged to behave like sodium trithiocarbonate when dissolved in water.The preparation of aqueous solutions of the tri- and tetrathiocarbonateof magnesium and strontium was alleged, but the magnesium thiocarbonateswere not isolated.

The previously noted paper by Mills and Robinson shows the preparationof ammonium thiocarbonate by digesting ammonium pentasulfide (obtainedby suspending sulfur in aqueous ammonia, then saturating with hydrogensulfide) with carbon disulfide. A crystalline residue from the reactionwas found to be ammonium perthiocarbonate. The authors prepared a"better" ammonium perthiocarbonate product, however, by extracting theammonium pentasulfide with carbon disulfide in a Soxhlet apparatus.

Stone et al disclose several methods for preparing solid ammonium,alkali and alkaline earth metal salts of tri- and"tetraperoxythiocarbonates," hereinafter referred to simply as"tetrathiocarbonates." One such method involves the solution of anactive metal such as sodium in anhydrous ethanol to form an ethoxidewhich, in turn, is reacted with hydrogen sulfide and carbon disulfide toform sodium trithiocarbonate. They report, however, that thetrithiocarbonates tend to be quite soluble in ethanol, and if it isdesired to recover the solid material from the solution, it is necessaryto treat the reaction mixture with a "displacing agent" such as ether,in which case the thiocarbonates frequently separate, not as solids, butas difficulty crystallizable oils which appear to be saturated aqueoussolutions of the trithiocarbonate salt. Consequently, such a procedureis not considered feasible for use on a commercial scale. Similarproblems were reported with tetrathiocarbonate salts, which wereprepared by reacting a metal sulfide such as sodium sulfide with sulfurand carbon disulfide, using procedures analogous to those for thetrithiocarbonates.

These problems were reportedly solved by carrying out the preparationreaction "in a medium which is composed of a major part of a nonsolventfor the reaction components and which contains only a minor proportion,less than sufficient to dissolve the inorganic sulfide, of a liquidwhich is miscible with said nonsolvent and which is a solvent, to ameasurable degree, for the inorganic sulfides." For the reaction medium,the preferred nonsolvents comprise between about 70 and about 90 percentof one or more relatively low boiling hydrocarbon materials such ashexane, cyclohexane and benzene, with the second solvent preferablybeing between about 10 and about 30 percent ethanol, isopropanol ordioxane. Stone et al report that it is not necessary for the secondsolvent to be anhydrous and that the "usual" 95-5 commercial azeotropeof ethanol and water is quite satisfactory to produce hydrated saltssuch as Na₂ CS₃.3H₂ O, although the alcohol produces the aforementioned"oil" when used alone.

Basic physical and chemical properties of these materials and a numberof basic method for making them are summarized in considerable detail,starting at page 154 of "Carbon Sulfides and their Inorganic and ComplexChemistry" by G. Gattow and W. Behrendt, Volume 2 of "Topics in SulfurChemistry" A. Senning, Editor, George Thieme Publishers, Stuttgart,1977. However, regardless of which material is made and how it isproduced, one common characteristic of the solid salts of tri- andtetrathiocarbonic acid is their relatively poor long term stability andmany tri- and tetrathiocarbonate salts will decompose and release carbondisulfide upon exposure to water or air, often within a few hours oreven minutes. This is not necessarily bad, if one wishes to use thereleased CS₂ as a soil fumigant and nematicide. However, where it isdesired to provide solid materials for such uses as lubrication orrubber additives, or "dry land" farming, etc., it is necessary that theybe produced in one or more forms which provide for and maintain the longterm stability of these salts when so used. As disclosed in copendingU.S. patent application Ser. Nos. 253,139 and 260,912, one method ofstabilizing these salts is to coat the solid particles with an oil orgrease. Another is to prepare the salts under completely anhydrousconditions and then store the resultant materials under a dry, inert gassuch as argon, hydrogen or, preferably, nitrogen until they are put intouse. What is needed are improved methods to prevent their decompositionunder ambient conditions. The present invention provides such methods.

SUMMARY OF THE INVENTION

In its broadest aspects, the present invention comprises stabilizedsolid particles of one or more salts, thioesters or complexes of athiocarbonate and a method for making same. The thiocarbonate speciesused are those which show short or long term degradation in the presenceof water, CO₂ or O₂ and said method comprises first putting saidparticles into a condition in which they are presently substantiallyfree of water, CO₂ and O₂ and then encapsulating them in a coating toprotect them from future contact with air and water. Preferably themethod comprises the steps of:

(1) forming said particles in a medium in which said thiocarbonate isstable and substantially insoluble;

(2) separating said particles from said medium so that said particlesare substantially water-free and in an environment which issubstantially free of water, CO₂ and O₂ ; and

(3) encapsulating said particles with a coating to protect them fromfuture contact with air and water.

As used herein, the term "water-free," when applied both to thestabilized solids of the present invention and to the media in whichsaid stabilized solids are prepared, shall mean that the water contentthereof is below the amount which would cause observable decompositionor hydrolysis of an unprotected thiocarbonate which is dissolved orsuspended therein or which results in the formation and separation of anaqueous solution of said solids. Also, as used herein, the term"thiocarbonate" shall mean those compounds containing a group of thegeneral formula:

    (C.sub.a S.sub.b)

wherein a is between about 1 and about 4 and b is between about 3 andabout 9 and (C_(a) S_(b)) is present as the anionic moiety in a salt, asthe acidic moiety of a thioester, or as a ligand in a metallic complex.The term "complex" shall refer to any compound in which (C_(a) S_(b))acts as a complexing ligand.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises stabilized solid thiocarbonate salts,thioesters and complexes, and methods for making same. The salts andthioesters of this invention have the general formula M_(c) (C_(a)S_(b))_(y) wherein a, the number of carbon atoms therein, ranges betweenabout 1 and about 4, preferably between about 1 and about 3, and morepreferably is 1, b, the number of sulfur atoms therein, ranges betweenabout 3 and about 9, preferably between about 3 and about 6, and morepreferably is 3 or 4, M is hydrogen, a cationic salt-forming moiety oran organic thioester forming radical, y is the valence of M and c is thevalence of (C_(a) S_(b)).

A first embodiment of the present invention is directed to a method formaking and storing stable salts and thioesters of tri- andtetrathiocarbonic acid. Although hydrogen sulfide and carbon disulfidewould be expected to react to form trithiocarbonic acid according to thereaction:

    H.sub.2 S+CS.sub.2 →H.sub.2 CS.sub.3                ( 2)

such is not the case. Consequently, other approaches to makingderivatives of the thiocarbonic acids must be used. One method formaking alkaline earth and heavy metal salts is by reacting a suitablesalt, such as the acetate, with a stable solution of an ammoniumthiocarbonate, such as that prepared by the procedure of Example 1 inU.S. Pat. No. 4,726,144, the teachings of which are incorporated hereinin their entirety, by reference, to precipitate an insoluble saltproduct.

Solid trithiocarbonate salts and thioesters useful for the purposes ofthe present invention are preferably prepared by reacting a mixture,preferably a stoichiometric mixture, of carbon disulfide and a source ofsulfide of the form M₂ S_(y), wherein M is a positive salt-formingmoiety or the organic moiety of a mercaptan and y is the valence of M,said reaction being performed under conditions sufficient to produce atrithiocarbonate salt or thioester according to the general reaction:

    M.sub.2 S.sub.y +y CS.sub.2 →M.sub.2 (CS.sub.3).sub.y( 3)

This reaction may be carried out at any temperature from 0° C. to theboiling point of carbon disulfide, and preferably from about 15° C. toabout 35° C. The reaction is preferably carried out under an inert orreducing gas atmosphere to avoid oxidation of any of the sulfurcompounds to sulfur oxide moieties such as thiosulfate.

Suitable cationic salt-forming moieties for M are ammonium, quaternaryammonium, quaternary phosphonium, quaternary arsonium, metals and metalcomplexes formed with commonly known ligands such as ammonia,ethylenediamine, diethylenetriamine, propylenediamine and pyridine.Preferably these moieties are ammonium or metals, more preferablyalkaline earth or alkali metals, most preferably ammonium, sodium orpotassium, and very most preferably potassium.

Suitable thioester forming organic moieties for M are alkyl, cycloalkyl,aryl, arylalkyl or alkylaryl groups, preferably alkyl groups having from1 to about 8 carbon atoms, more preferably alkyl groups having 1 toabout 5 carbon atoms, and most preferably alkyl groups having between 1and about 3 carbon atoms.

The presence of significant amounts of water in the reaction vesseloften tends to cause the formation of pasty, crusty, oil-like saltdeposits therein, which are removable only with the greatest difficulty.Moreover, even for thiocarbonate species which are nominally insolublein water, long-term exposure to water will often cause some degree ofdegradation. Consequently, the above reaction preferably takes place ina water-free liquid medium, which, while being a solvent for the sourceof sulfide, does not dissolve, to any great extent, the thiocarbonatesalt or ester formed by this reaction, thus allowing it to precipitateout for subsequent recovery.

While any "water-free" solvent for the source of sulfide may be used,the preferred solvents in which to perform this reaction are the lowermolecular weight, saturated absolute alcohols such as methanol, ethanol,propanol, isopropanol, n-butanol, isobutanol and secondary butanol. Suchalcohols offer the advantages of (1) being commercially available in awater-free, absolute condition at low cost, (2) being miscible withcarbon disulfide, and (3) being relatively good solvents for the metalsulfides, mercaptans and acetates used. The particular alcohol useddepends on the particular end-product desired. For example, where theend-product is an alkali metal trithiocarbonate, particularly sodium andpotassium trithiocarbonate, the relatively high solubility of thesesalts in methanol and ethanol would dictate that an alcohol wherein saidsalt is much less soluble such as isopropanol or, preferably, n-butanolbe used.

Where an alcohol is used as the water-free solvent, one convenient wayof forming the source of sulfide is the reaction of hydrogen sulfidewith a metal alkoxide of the form M(OA)_(y), wherein A is an alkylradical and y is the valence of M. This alkoxide is generated in-situeither by dissolving a reactive metal, preferably an alkali or analkaline earth metal, more preferably an alkali metal, most preferablysodium or potassium, and, very most preferably, potassium, or a reactivehydroxide, preferably an alkali metal hydroxide, most preferably sodiumor potassium and, very most preferably, potassium hydroxide, in thealcohol according to the reactions:

    2K+2AOH→2KOA+H.sub.2                                ( 4)

or, preferably, by:

    KOH+AOH→KOA+H.sub.2 O                               (5)

Because of the aforementioned sensitivity of the potassiumthiocarbonates to the presence of water, it is necessary that the watergenerated in reaction (5) be removed prior to any further processing.One approach for so doing is to heat the solution to a temperature highenough for an alcohol-water azeotrope to form and boil off. Anotherapproach is to pass the solution through an absorbent, such as amolecular sieve, which is useful for separating out the water.

After the water is removed, passing hydrogen sufide through theremaining solution will convert the alkoxide to said source of sulfur,after which the addition of carbon disulfide, as shown in equation (3)above, will complete the reaction. Where the cationic salt-formingmoiety is to be an alkaline earth or a heavy metal such as iron, copper,nickel, zinc, lead, or cadmium, such a salt can be made by reacting thepotassium thiocarbonate salt, as just formed in the water-free medium,with an alcohol soluble salt such as the acetate of the moiety, which issubsequently added thereto. To do this, alcohols such as methanol andethanol, which are capable of dissolving substantially all of both thealkali metal trithiocarbonate and the heavy metal acetate, arepreferred.

The stable tetrathiocarbonate salts and thioesters of this invention areprepared in a similar manner, with the general reaction defined inequation (3) above being:

    y S+M.sub.2 S.sub.y +y CS.sub.2 →M.sub.2 (CS.sub.4).sub.y( 6)

A second preferred embodiment of the present invention is the formationof one or more stabilized thiocarbonate complexes of the form:

    (CI).sub.x (M.sub.z (C.sub.a S.sub.b).sub.y)

wherein M is a cationic complex-forming metal such as tin, lead, or atransition metal such as iron, cobalt, nickel, platinum, copper, zinc,cadmium, mercury, chromium, manganese, molybdenum, etc., CI is aneutralizing counter ion such as quaternary ammonium, quaternaryarsonium, quaternary phosphonium or quaternary stibonium, a is thenumber of carbon atoms in the complex, ranging between 1 and about 4, bis the number of sulfur atoms in the complex, ranging between about 3and about 9, x is the number of counter ions necessary to neutralize thecomplex, y is the number of thiocarbonate groups in the complex and z isthe number of cationic complex forming moieties in the complex.

One method for the preparation of such complexes is by reacting amixture of an alkali metal thiocarbonate, prepared as described above,with a soluble complex forming moiety and a soluble cationic counterion, preferably one containing quaternary ionic groups of the form:##STR1## with Q being nitrogen, arsenic, antimony or phosphorus, andwith each R group being separately and independently hydrogen or,preferably an organic radical, said organic radical preferably being analkyl, aryl, cycloalkyl or alkylaryl group having up to about 50 carbonatoms. It is understood that other cationic counter ionic moieties suchas alkali and alkaline earth metals may be substituted for thequaternary moieties, for example, by ion exchange techniques.

The invention comprises the preparation and use of still otherstabilized thiocarbonate compositions. Among the thiocarbonates suitablefor this purpose are the metal salts of organic radical substitutedthioesters such as potassium methyl trithiocarbonate, alkyl dimershaving the forms (MCS₃)₂ and (MCS₄)₂, and salts and esters of thegeneral form M₂ (C₃ S₅)_(y), wherein y is the valence of M, as well ascomplexes made therewith. Still other solid carbon-sulfur compoundswithin the broad definition given above and methods for synthesizingthem can be found in any advanced treatise on carbon-sulfur chemistry.Where such compounds prove to be sensitive to water, CO₂ or O₂, they toocan be stabilized by the method of the present invention.

The second step in the preparation of the stabilized solid compositionsof the present invention is the separation of the precipitated salt,thioester or complex product from the reaction medium. There are anumber of methods suitable for such separation, including filtration andcentrifuging. Whichever is used, the major factors of concern are theremoval of any water in the medium so that at the conclusion thereof theparticles are substantially water-free, and in an environment which issubstantially free of degradative media such as oxygen, carbon dioxideand/or water. Once separated, any residual reactants can be removed withone or more washings with an inert solvent miscible with alcohol andcarbon disulfide, such as pentane, hexane, and ether, either alone or ina mixture with fresh alcohol. Since it avoids the introduction of other,foreign materials into the process, a mixture of fresh alcohol andcarbon disulfide is preferred. Where the separated particles wereprepared in a water-containing medium, absolute ethanol in particular,offers the advantage of being miscible with water and, therefore,readily removing it.

The washed product may be dried to form freely flowing particles atmoderate temperatures, either under vacuum or under a flowing stream ofan inert gas such as argon, hydrogen or, preferably nitrogen. Onceseparated and dried, the solid product may be safely stored in opaque,sealed containers, preferably under a dry nitrogen atmosphere.

For an application, such as agricultural use in irrigated fields, suchprotective storage is quite adequate to keep the solids in propercondition until they are needed. However, there are many others wherethe particles must either survive for long periods of time, either inthe open air or in contact with water, or decompose, in a controlledmanner, over some period of time. Such uses include anti-wear/extremepressure additives for petroleum base lubricants and, particularly wateremulsified cutting oils. Another use is as a general agriculturalpesticide in non-irrigated areas. In these and other situations wherecontact with air or water is expected, the solid particles must becoated with one or more materials capable of either preventing contactof the solid particles with the surrounding environment or controllingthe degree to which such contact shall occur.

There are a number of final coating methods which can be used, dependingupon the particular needs being addressed. For example, for agriculturaluse, the particles may be coated with a biodegradable coating such as awax which may be applied either by contacting the particles with a waxsolution in a low boiling hydrocarbon solvent, and then heating themixture to drive off the solvent, or by contacting the particles withthe molten wax under conditions adapted to keep the protected salt orcomplex in particulate form. Upon depositing the thus coated solids inthe soil, the wax coating could be removed either by natural weatheringor by attack by soil bacteria and other organisms, with the result that,over time, the particles would be exposed to the environment anddecompose to form a soil pesticide.

Where longer term survival in agricultural use is desired, the particlesmay be encapsulated with sulfur, again either by being contacted by asulfur solution in carbon disulfide or with molten sulfur. Such anapplication would be highly advantageous since sulfur is also widelyused for pH control and other soil conditioning purposes, so a singleapplication of particles so coated would serve two purposes--soilconditioning and long term pest control. Experience has shown thatsulfur coatings tend to be brittle and will, on occasion, crack, thusexposing the coated particles to outside air and moisture. Where suchcracking has been observed, it is found that applying a second coatingof petrolatum to the particles will fill the cracks with an air-tightmaterial, which, like the sulfur, is readily biodegradeable.

Where the particles are to be used as an extreme pressure/anti-wearadditive, other approaches can be used. For machine oils and greases,merely coating the particles with a water-free oil or grease willusually serve to keep thiocarbonate salts and complexes fromdecomposing. Where the particles are to be used as extreme pressureadditives in water-containing media such as emulsified cutting oils,other approaches must be used. Preferably, such coatings arepolymerizable monomers, such as methyl methacrylate, or polymerizablenatural oils such as linseed or tung oil. These polymers will formsturdy water and air tight coatings which will protect the encapsulatedparticles until they are crushed beneath the tool tip at the point ofextreme-pressure contact. In such using, it is preferred that thepolymer be substantially non-biodegradable.

The invention will be further described with reference to the followingexamples which are provided to illustrate and not limit the presentinvention.

EXAMPLE 1

Twenty grams (0.36 moles) of reagent grade potassium hydroxide was addedto 200 grams (255 cc) of absolute ethyl alcohol, with the mixture beingrefluxed until all of the KOH had dissolved (approximately 1 hour),after which the water formed was removed by a conventional water-alcoholazeotropic distillation. After adding a sufficient amount of absolutealcohol to bring the alcoholic solution back up to about 250 cc andcooling the solution back to room temperature, 5.7 grams (0.18 moles) offinely divided sulfur was added, with stirring, after which 6.1 grams(0.18 moles) of hydrogen sulfide was dissolved therein. At theconclusion of this addition, the temperature of the exothermicallyheated solution was adjusted to about 130° F. and 13.6 grams (0.19moles) of carbon disulfide were added, dropwise, thereto over a periodof about 30 minutes. The mixture was then heated, under reflux, withstirring, for between about 20 minutes and about 1 hour, after whichtime a yellow-orange precipitate of potassium tetrathiocarbonate formed.The precipitate was vacuum filtered, under an inert atmosphere, andwashed 3 times with about 50 cc of pentane. The washed material wasdried, under vacuum, for about 8 hours at 60° C., to producefree-flowing salt particles.

EXAMPLE 2

Nine grams of zinc sulfate monohydrate (0.05 moles) and 45 grams ofbenzyl triphenyl phosphonium chloride (0.107 moles) were dissolved in1200 cc of deionized water. After filtration to remove a small amount ofinsoluble material there was added, at room temperature and withstirring, 300 cc of an aqueous solution containing 0.51 moles of sodiumtetrathiocarbonate prepared as described in U.S. Pat. No. 4,726,144. Ayellow precipitate formed which after being separated by filtration waswashed with water, ethanol and ether. After drying in a desiccator, thefree-flowing complex particles had a melting point of 145° to 152° C. Acomparison of the elemental analysis of the solid and for one having thetheoretical composition of ((C₆ H₅)₃ C₆ H₅ CH₂ P)₂ (CS₄)₂ Zn is asfollows:

    ______________________________________                                                     Actual                                                                              Theoretical                                                             wt. % wt. %                                                      ______________________________________                                        phosphorus     5.9     5.88                                                   carbon         59.6    59.32                                                  hydrogen       4.1     4.22                                                   sulfur         22.3    24.36                                                  zinc           5.9     6.21                                                   ______________________________________                                    

EXAMPLE 3

Twenty grams (0.36 moles) of reagent grade potassium hydroxide was addedto 200 grams (255 cc) of absolute ethyl alcohol, with the mixture beingrefluxed until all of the KOH had dissolved, after which the waterformed was removed by a conventional water-alcohol azeotropicdistillation. After adding a sufficient amount of absolute alcohol tobring the alcoholic solution back up to about 250 cc, and cooling thesolution back to room temperature, 7.4 grams (0.22 moles) of hydrogensulfide was added with vigorous stirring, followed by 13.6 grams (0.19moles) of carbon disulfide, which was added through a dropping funnel.The mixture was then stirred, at room temperature, for about 90 minutesduring which time a light yellow precipitate of potassiumtrithiocarbonate formed. The precipitate was vacuum filtered, under aninert atmosphere, and washed 3 times each with ethanol and ether. Thewashed material was dried, under vacuum, for about 8 hours at 60° C., toproduce free-flowing salt particles.

EXAMPLE 4

47.5 grams of commercial paraffin wax was brought to a temperature about10° F. above its melting point at which time 47.5 grams of the potassiumtetrathiocarbonate, as prepared in Example 1, and 5 grams of acommercial surfactant were added. The mixture was stirred for about 10minutes at 5,000 RPM using a Cowles disperser. The hot liquid suspensionwas poured onto release paper on a cold slab and was allowed to cool.The resulting block had good stability and there was only a faint odorof CS₂.

EXAMPLE 5

38 grams of the potassium tetrathiocarbonate, as prepared in Example 1,were mixed with 53 grams of heavy mineral oil and 9 grams of asurfactant which was soluble therein for about 10 minutes at 5,000 RPMusing a Cowles disperser. While there was slow settling of the initiallyuniform suspension, the material could be readily redispersed with onlymild agitation. There was a slow loss of CS₂ from the suspension ascompared with a rapid degradation and loss of CS₂ from the solidunprotected potassium tetrathiocarbonate when it was exposed to theatmosphere.

EXAMPLE 6

Potassium methyl trithicarbonate (K(CH₃ CS₃)) was prepared by combining2532 g (33.3 mole) of carbon disulfide, which had previously beenchilled to -5° C., with 265 g (4.0 mole) of 85% potassium hydroxide withstirring under a nitrogen atmosphere. Following the addition of the KOH,230 g (4.8 mole) of methyl mercaptan was added, dropwise, over a periodof about 4 hours, during which time the mixture was stirred andmaintained at a temperature of about 2° C., after which the mixture wasstirred, under nitrogen for an additional 16 hours. At the conclusion ofthis time about 3 liters of ether were added and the mixture stirred foran additional 24 hours, during which time a yellowish colored solidmaterial precipitated out. This was separated from the ether/CS₂ mixtureby vacuum filtration and dried, under vacuum for a period of about 4days. The yield was about 543 g of a material having the followinganalysis:

    ______________________________________                                                        Actual  Theoretical                                           (K(CH.sub.3 CS.sub.3))                                                                        wt. %   wt. %                                                 ______________________________________                                        carbon          15.1    14.8                                                  hydrogen         2.0     1.9                                                  ______________________________________                                    

To about 150 cc of absolute ethanol, with about 16.2 grams of thepotassium methyl trithiocarbonate, synthesized above, dissolved therein,was added about 12.7 grams of iodine dissolved in an additional 150 ccof absolute ethanol. The iodine solution was added dropwise at ambienttemperature with continuous stirring. At the conclusion of thisaddition, the reaction mixture was poured into about 1000 cc of coolwater, as a result of which a light yellow solid formed andprecipitated. This was filtered off and dried under reduced pressure.About 7.5 grams of solid was obtained with a melting point of 88°-89° C.A comparison of the elemental analysis of the solid and one having thetheoretical composition (CH₃ CS₃)₂ is as follows:

    ______________________________________                                                     Actual                                                                              Theoretical                                                             wt. % wt. %                                                      ______________________________________                                        carbon         18.5    19.5                                                   hydrogen        3.2     2.4                                                   sulfur         74.0    78.0                                                   ______________________________________                                    

Obviously many modifications and variations of this invention, as hereinabove set forth, may be made without departing from the spirit and scopethereof, and therefore only such limitations should be imposed as areindicated in the following claims. All embodiments which come within thescope and equivalency of the claims are, therefore, intended to beembraced therein.

We claim:
 1. A method for making stabilized solid particles of athiocarbonate selected from the group consisting of alkali and alkalineearth metal tri- and tetrathiocarbonates, and combinations thereof, saidmethod comprising the steps of:(1) forming particles of a thiocarbonateselected from alkali and alkaline earth metal tri- andtetrathiocarbonates generally unstable in soil in a water-free medium inwhich said thiocarbonate is stable and substantially insoluble; (2)separating said particles from said medium so that said particles aresubstantially water-free and in an environment which is substantiallyfree of water, CO₂ and O₂ ; and (3) dispersing said particles in amatrix selected from the group consisting of water-resistant wax, oil,grease, and combinations thereof in an amount sufficient to increase thestability of said thiocarbonate in soil.
 2. The method of claim 1wherein said thiocarbonate is of the form:

    M.sub.c (C.sub.a S.sub.b).sub.y

wherein M is a cationic salt forming moiety, a ranges between 1 andabout 4, b ranges between about 3 and about 9, c is the valence of(C_(a) S_(b)) and y is the valence of M
 3. The method of claim 2 whereina ranges between 1 and 3, b ranges between 3 and 5, and c is 1 or
 2. 4.The method of claim 2 wherein a is 1, b is 3 or 4 and c is
 2. 5. Themethod of claim 4 wherein M is a cationic salt-forming moiety selectedfrom the group consisting of ammonium, quaternary ammonium, quaternaryphosphonium, quaternary arsonium, metals and metal complexes formed withammonia, ethylenediamine, diethylenetriamine, propylenediamine andpyridine.
 6. The method of claim 4 wherein M is selected from the groupconsisting of ammonium, alkaline earth metals and alkali metals.
 7. Themethod of claim 2 wherein M is an alkali metal.
 8. The method of claim 2wherein M is alkali metal.
 9. The method of claim 7, wherein said alkalimetal is selected from sodium, potassium, and combinations thereof. 10.The method of claim 1 wherein said thiocarbonate salt comprises thereaction product of carbon disulfide and a source of sulfide of the formM₂ S_(y), wherein M is a cationic salt-forming moiety, and y is thevalence of M, said reaction being performed in a liquid water-freemedium under conditions sufficient to produce a trithiocarbonate salt ofthe general form M₂ (CS₃)_(y).
 11. The method of claim 10 wherein saidliquid water-free medium is selected from the group consisting ofmethanol, ethanol, propanol, isopropanol, n-butanol, isobutanol andsecondary butanol.
 12. The method of claim 10 wherein said source ofsulfide is produced by the steps of:a) reacting an alkali metalhydroxide with a water-free alcohol selected from the group consistingof methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol andsecondary butanol, to form a solution of an alkoxide of the form, MOA,wherein M is an alkali metal radical and A is an alkyl group; andreacting said alkoxide with hydrogen sulfide to form said source ofsulfide.
 13. The method of claim 1 wherein said thiocarbonate saltcomprises the reaction product of a source of sulfide of the form M₂S_(y), wherein M is a cationic saltforming moiety, and y is the valenceof M, with a mixture of elemental sulfur and carbon disulfide, saidreaction being performed in a liquid water-free medium under conditionssufficient to produce a tetrathiocarbonate salt of the general form M₂(CS₄)_(y).
 14. The method of claim 13 wherein said liquid water-freemedium is selected from the group consisting of methanol, ethanol,propanol, isopropanol, n-butanol, isobutanol and secondary butanol. 15.The method of claim 13 wherein the source of sulfur, elemental sulfurand carbon disulfide are present in a stoichiometric mixture for thegeneral reaction:

    M.sub.2 S.sub.y +yS+yCS.sub.2 =>M.sub.2 (CS.sub.4).sub.y.


16. The method defined in claim 1, wherein, in step (3), saidthiocarbonate particles are dispersed in a water-resistant wax.
 17. Amethod for making stabilized solid particles of a thiocarbonate salt ofthe form:

    M.sub.2 (CS.sub.b).sub.y

wherein M is selected from the group consisting of alkali metals,alkaline earth metals, and combinations thereof, b is an integer betweenabout 3 and about 5, and y is the valance of M, said salt beinggenerally unstable in soil, said method comprising the steps of: (1)forming said particles in a water-free liquid medium in which saidthiocarbonate salt is substantially insoluble; (2) separating saidparticles from said medium so that said particles are substantiallywater-free and in an environment which is substantially free of water;CO₂ and O₂ ; and (3) dispersing said particles in a matrix selected fromthe group consisting of water resistant wax, oil, grease, andcombinations thereof the relative proportions of said thiocarbonate saltand said matrix being sufficient to provide sufficient thiocarbonate tofumigate soil and sufficient matrix to reduce the rate of decompositionof said thiocarbonate salt when said particles are applied to soil. 18.The method of claim 17 wherein b is 3 and step (1) comprises the stepsof:a) reacting an alkali metal hydroxide with a water-free alcoholselected from the group consisting of methanol, ethanol, propanol,isopropanol, n-butanol, isobutanol and secondary butanol, to form asolution of an alkoxide of the form, MOA, wherein M is an alkali metalradical and A is an alkyl group; b) reacting said alkoxide with hydrogensulfide to form a source of sulfide; and c) reacting said source ofsulfide with carbon disulfide to form an alkali trithiocarbonate salt.19. The method of claim 17 wherein b is 4 and step (1) comprises thesteps of:a) reacting an alkali metal hydroxide with a water-free alcoholselected from the group consisting of methanol, ethanol, propanol,isopropanol, n-butanol, isobutanol and secondary butanol, to form asolution of an alkoxide of the form, MOA, wherein M is an alkali metalradical and A is an alkyl group; b) reacting said alkoxide with hydrogensulfide to form a source of sulfide and c) reacting said source ofsulfide with a mixture of sulfur and carbon disulfide to form an alkalitetrathiocarbonate salt.
 20. The method defined in claim 17, wherein Mis alkali metal, b is 3 or 4, or a value between 3 and 4, and y is 1.21. The method defined in claim 20, wherein said alkali metal isselected from sodium, potassium, and combinations thereof.
 22. Themethod defined in claim 20, wherein said thiocarbonate salt comprises atetrathiocarbonate.
 23. The method defined in claim 17, wherein M is analkaline earth metal, b is 3 or 4, or a value between 3 and 4, and y is2.
 24. The method defined in claim 17, wherein, in step (3), saidthiocarbonate particles are dispersed in a water-resistant wax.
 25. Amethod for making stabilized solid particles of a tetrathiocarbonatesalt generally unstable in soil, of the form:

    M.sub.2 (CS.sub.4).sub.y

wherein M is a cationic salt forming moiety, and y is the valence of M,said method comprising the steps of: (1) forming said particles in awater-free liquid medium in which said thiocarbonate salt issubstantially insoluble; (2) separating said particles from said mediumso that said particles are substantially water-free and in anenvironment which is substantially free of water, CO₂ and O₂ ; and (3)dispersing said particles in a matrix selected from the group consistingof water resistant wax, oil, grease, and combinations thereof therelative proportions of said thiocarbonate salt and said matrix beingsufficient to completely encompass said thiocarbonate salt within saidmatrix and substantially increase the stability of said thiocarbonatesalt when said particles are applied to soil.
 26. The method of claim 25wherein step (1) comprises the steps of:a) reacting an alkali metalhydroxide with a water-free alcohol selected from the group consistingof methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol andsecondary butanol, to form a solution of an alkoxide of the form, MOA,wherein M is an alkali metal radical and A is an alkyl group; b)reacting said alkoxide with hydrogen sulfide to form said source ofsulfide; and c) reacting said source of sulfide with a stoichiometricamount of sulfur and carbon disulfide for the general reaction:

    M.sub.2 S.sub.y +yS+yCS.sub.2 =>M.sub.2 (CS.sub.4).sub.y.


27. The method defined in claim 25, wherein M is an alkali metal, b is 3or 4, or a value between 3 and 4, and y is
 1. 28. The method defined inclaim 27, wherein said alkali metal is selected from sodium, potassium,and combinations thereof.
 29. The method defined in claim 28, whereinsaid thiocarbonate salt comprises a tetrathiocarbonate.
 30. The methoddefined in claim 25, wherein M is an alkaline earth metal, b is 3 or 4,or a value between 3 and 4, and y is
 2. 31. The method defined in claim25, wherein, in step (3), said thiocarbonate particles are dispersed ina water-resistance wax.